The present invention relates to the stabilization of subterranean formations. More particularly, the present invention relates to methods for stabilizing unconsolidated portions of a subterranean formation and controlling the production of water from those portions.
Hydrocarbon wells are often located in subterranean formations that contain unconsolidated particulates that may migrate out of the subterranean formation with the oil, gas, water, and/or other fluids produced by the wells. The presence of particulates, such as formation sand and even loose proppant, in produced fluids is undesirable in that the particulates may abrade pumping and other producing equipment and reduce the fluid production capabilities of the producing zones. Unconsolidated portions of a subterranean formation include those that contain loose particulates and those wherein the bonded particulates have insufficient bond strength to withstand the forces created by the production of fluids through the formation.
One method of controlling particulates in such unconsolidated portions has been to produce fluids from the formations at low flow rates, so that the near well stability of sand bridges and the like may be substantially preserved. The collapse of such sand bridges, however, may occur due to unintentionally high production rates and/or pressure cycling as may occur from repeated shut-ins and start ups of a well. The frequency of pressure cycling is critical to the longevity of the near well formation, especially during the depletion stage of the well when the pore pressure of the formation has already been significantly reduced.
Another method of controlling particulates in unconsolidated formations involves placing a filtration bed containing gravel near the well bore to present a physical barrier to the transport of unconsolidated formation fines with the production of hydrocarbons. Typically, such “gravel-packing operations” involve the pumping and placement of a quantity of a desired particulate into the unconsolidated formation in an area adjacent to a well bore. One common type of gravel-packing operation involves placing a gravel-pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The gravel-pack screen is generally a filter assembly used to retain the gravel placed during the gravel-pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel-pack sand used. Similarly, a wide range of sizes of gravel is available to suit the characteristics of the unconsolidated particulates in the subterranean formation. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow. When installing the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a viscous treatment fluid. Once the gravel is placed in the well bore, the viscosity of the treatment fluid is reduced, and it is returned to the surface.
Gravel packs act, inter alia, to stabilize the formation while causing minimal impairment to well productivity. The gravel, inter alia, acts to prevent formation particulates from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the production tubing. Such packs may be time consuming and expensive to install. Due to the time and expense needed, it is sometimes desirable to place a screen without the gravel. Even in circumstances in which it is practical to place a screen without gravel, it is often difficult to determine an appropriate screen size to use as formation sands tend to have a wide distribution of grain sizes. When small quantities of sand are allowed to flow through a screen, formation erosion becomes a significant concern. As a result, the placement of gravel as well as the screen is often necessary to assure that the formation sands are controlled. Expandable sand screens have been developed and implemented in recent years. As part of the installation, an expandable sand screen may be expanded against the well bore, cased hole, or open hole for sand control purposes without the need for gravel packing. However, screen erosion and screen plugging are the main disadvantages of expandable screens.
Another method used to control particulates in unconsolidated formations involves consolidating unconsolidated subterranean producing zones into stable, permeable masses by applying a resin followed by a spacer fluid, a catalyst, and an after-flush fluid. Such resin application may be problematic when, for example, an insufficient amount of spacer fluid is used between the application of the resin and the application of the external catalyst. The resin may come into contact with the external catalyst in the well bore itself rather than in the unconsolidated subterranean producing zone. When resin is contacted with an external catalyst an exothermic reaction occurs that may result in rapid polymerization, potentially damaging the formation by plugging pore channels, halting pumping when the well bore is plugged with solid material, or resulting in a downhole explosion as a result of the heat of polymerization. Also, using these conventional processes to treat long intervals of unconsolidated regions is not practical due to the difficulty in determining if the entire interval has been successfully treated with both the resin and the external catalyst. Further, conventional consolidation techniques have often resulted in limited or inadequate penetration distances of consolidating agent into formations.
Often, unconsolidated formation sands migrate out of the formation when water is produced from the formation. This migration of formation sands is due, in part, to the fact that most natural cementation between formation sand grains disintegrates when in contact with an aqueous moving phase. The production of water from a subterranean producing zone is disadvantageous due to its effect on mobilizing formation sands, and because water production constitutes a major expense in the recovery of hydrocarbons from subterranean formations, especially in light of the energy expended in producing, separating, and disposing of the water.